In optical communications networks, optical transceiver modules are used to transmit and receive optical signals over optical fibers. On the transmit side of a transceiver module, a light source (e.g., a laser diode) generates amplitude modulated optical signals that represent data, which are received by an optics system of the transceiver module and focused by the optics system into an end of a transmit optical fiber. The signals are then transmitted over the transmit fiber to a receiver node of the network. On the receive side of the transceiver module, the optics system of the transceiver module receives optical signals output from an end of a receive optical fiber and focuses the optical signals onto an optical detector (e.g., a photodiode), which converts the optical energy into electrical energy.
The transmit and receive fiber cables have connectors on their ends, often LC connectors, that are adapted to mate with transmit and receive receptacles, respectively, formed in the transceiver module. A variety of optical transceiver module configurations are used in optical communications network. Some optical transceiver modules have multiple transmit receptacles and multiple receive receptacles for connecting multiple receive and transmit fiber cables to the module. Some transceiver modules having a single receive receptacle and a single transmit receptacle arranged side by side for connecting a single receive fiber cable and a single transmit fiber cable, respectively, to the transceiver module.
The transceiver modules themselves also have mating elements on them that are adapted to mate with mating elements formed on the cages. The cages are contained in racks, and each rack typically includes many cages that are arranged in very close proximity to one another. Each of these cages is configured to receive a transceiver module on the front side of the rack through a front panel of the rack. The transceiver modules are configured so that they may be inserted into and removed from the cages. The modules typically include latching mechanisms that couple to mating features on the cages when the modules are inserted into the cages. In order to remove a module from a cage, the module must be de-latched to decouple the latching mechanism from the features on the cage, which can be challenging when the modules are spaced closely together in the racks.
A variety of different latching mechanism configurations are used on optical transceiver modules. In general, latching mechanisms used on optical transceiver modules include spring loading elements that maintain the latching mechanisms in their locked positions via spring forces. These types of latching mechanisms typically include a bail that is moved to a locked position in order to latch the module to the cage and that is moved to an unlocked position in order to de-latch the module from the cage. When the bail is in the locked position, a latch lock pin extends through an opening formed in the cage to prevent movement of the module relative to the cage and relative to the LC connectors connected to the transmit and receive receptacles. When the bail is in the locked position, the latch lock pin is retracted from the opening formed in the cage, making it possible to remove the module from and insert the module into the cage.
In general, the transmit and receive receptacles of optical transceiver modules are areas in the transceiver modules that allow electromagnetic interference (EMI) to escape from the transceiver modules. The Federal Communications Commission provides standards that limit the amount of electromagnetic radiation that may emanate from unintended sources. A variety of techniques and designs are used to shield potential EMI openings in optical transceiver modules in order to limit the amount of EMI radiation that may pass through the openings and thereby propagate into the environment outside of the modules. The transmit and receive receptacles contain portions of transmit and receive fiber optic ports, respectively, that mate with the transmit and receive connectors, respectively, when the connectors are plugged into the receptacles. In some known optical transceiver module designs, the ports are made of metal in order to help shield EMI. Although the use of metal ports helps to shield EMI, the use of metal ports is insufficient, in and of itself, to provide an effective EMI solution.
In order to effectively shield EMI, the metal ports need to be in consistent electrical contact with the metal housing of the transceiver module. The effective size of an EMI aperture is generally equivalent to the longest single dimension of non-contact between the port and the housing. If, for example, parts of the port along its circumference are not in contact with the housing, the EMI aperture size will be equal to the largest circumferential part over which the port and the housing are not in contact with each other. Often times, electrically conductive adhesive is used to fill in gaps between the ports and the housing to provide continuous conductive contact between the ports and the housing.
Because metal ports are relatively expensive, the transmit and receive ports are sometimes made of plastic. When the ports are made of plastic, the ports essentially constitute EMI openings that are very large in size. Although electrically conductive adhesive is normally used to seal the ports and provide EMI shielding, the EMI apertures that result when plastic ports are used are still relatively large in size. EMI aperture size is inversely related to the frequency of the transceiver module. Therefore, for transceivers that operate at low frequencies have maximum allowable EMI aperture sizes that are larger than transceivers that operate at higher frequencies. For example, a transceiver that operates at 1 Gigabits per second (Gb/s) can have an EMI aperture that is twice as large as that of a transceiver that operates at 10 Gb/s. Consequently, plastic ports generally are not suitable for use with transceivers that operate at high frequencies (e.g., 10 Gb/s).
Another problem with known transceiver module designs that rely on covering the ports with electrically conductive adhesive to provide adequate EMI shielding is that the adhesive prevents the ports from floating. Floating port designs are sometimes used because they allow some movement of the ports within the receptacles. When the connectors are plugged into the receptacles, the floating ports automatically align with the connectors, thereby obviating the need to use active alignment processes to align the ports with the connectors. Because the use of electrically conductive adhesive generally prevents the ports from floating, an active alignment process is typically performed while the adhesive is being applied, which is difficult and time consuming.
Accordingly, a need exists for an EMI system that is satisfactory at sealing fiber optic ports of an optical transceiver module. A need also exists for an EMI system that is satisfactory at sealing fiber optic ports of an optical transceiver module, and which also allows the ports to float.